Study on Microbes Found on International Space Station Is "Quite a Relief"

It was a bit alarming when in November, scientists isolated five strains of microbes from a toilet aboard the International Space Station. Some of the bacteria contained antibiotic resistance genes, much like the type that are giving rise to dangerous superbugs on Earth. The safety of our spacebound compatriots seemed to be in great danger until Tuesday, when a paper in mSystems gave everyone involved a reason to relax — at least for now.

It’s quite a relief to see that the bacteria we looked at seem quite normal.

Led by Erica Hartmann, an assistant professor at Northwestern University’s McCormick School of Engineering, the paper shows that the vibrant community of microbes aboard the ISS is definitely adapting to the harsh conditions of space, but not in a way that will threaten the astronauts on the ISS.

Though Hartmann and her team investigated different strains of ISS bacteria than those identified in November — Bacillus cereus and Staphylococcus aureus — the findings still apply to the ISS bugs.

“It’s quite a relief to see that the bacteria we looked at seem quite normal—although again, we don’t know for sure that these findings will hold for all bacteria,” Hartmann tells Inverse.

Astronauts working in space live and work in close quarters, so it would be hard to stop infections from spreading if they arise.

There has been a lot of speculation that space conditions might actually make microbes more harmful to humans, says Hartmann. In the early ‘80s, scientists found that E. coli aboard a French-Soviet manned flight developed antibiotic resistance far faster than expected. In 2016, colonies of Salmonella bacteria sent into space came back killed mice more efficiently than our Earthbound strains. But the new paper shows that space conditions don’t necessarily turn bacteria against humans.

“Because of the general concern, we expected we might find an uptick in virulence or other things that would make bacteria more harmful to humans,” she explains. Fortunately, her results showed something different: The types of genes that are being “selected for” aboard the ISS — that is, they provide advantages for the bacteria in that environment — don’t make bacteria dangerous to people.

There’s more than one bit of good news in the paper. While the study confirms that the ISS bacteria did carry genes that could confer resistance to antibiotics, the team shows that those genes probably indicate “intrinsic resistance” rather than acquired resistance. In other words, the microbes didn’t acquire the genes while they were in space; they had them even when they were on Earth.

What we should worry about in the future, she says, is “mobile resistance” — a type of gene that can be passed from bacteria to bacteria.

“If, however, it has a mobile resistance element (one or more genes), it could give that resistance to a different bacterium that does affect humans, and that could be a problem. But we didn’t see much evidence for mobile resistance in the ISS,” she says.

The International Space Station photographed by Expedition 56 crew members from a Soyuz spacecraft after undocking.

While the majority of the paper spells good news for astronauts, Hartmann cautions that there’s no guarantee the system can’t change, leading bacteria to eventually become either infectious to humans, and worse, resistant to antibiotics. On Earth, places like hospitals or animal feeding operations with high amounts of bacteria and antibiotic agents tend to be ground zero for superbugs. We should be aware of the similarities between those environments and the conditions aboard a spacecraft.

“Spacecraft are pretty tight spaces, and we rely on specific antimicrobials to decontaminate surfaces or life support systems or treat astronauts. So if bacteria developed resistance to the antimicrobials especially, say, on a long trip to Mars, it could be very problematic.”

At least for now, it seems like we’ve managed to sidestep that particular issue aboard the ISS. Astronauts and space microbes appear be co-existing peacefully.